Hydraulic fracturing is used to increase the area of a formation that is in communication with a wellbore and therefore increasing either production of fluids, or increasing the amount of fluids that may be injected into the formation from the wellbore. Hydraulic fracturing has been in commercial use for many decades, but gradual improvements in the size of fractures that can be created and the cost effectiveness of the fractures, along with developments like improved horizontal drilling and directional drilling, have resulted in hydraulic fracturing enabling production of hydrocarbons from formations such as source rocks or other very low permeability formations, that were previously not considered to be economically producible.
Typically, gas and/or oil is produced from low permeability formations such as source rocks, by providing horizontal wells in the formations for distances of a mile or more. The formation is then fractured from the wellbores in as many as twenty to fifty places, with the fractures placed every 15 to 150 meters along the horizontal wellbore. The fractures are provided by pumping fracturing fluids into an isolated section of the wellbore that is in communication with formation at pressures that exceed the pressure that causes the formation to break, and open up. This allows fracturing fluids to enter the formation through into the fracture and further propagate the fracture until the rate at which fluids go into the formation, via the rock faces of the fracture, equals the rate at which fluids can be pumped into the fracture.
Fractures are either propped open after they are formed by including in the fracturing fluids materials such as finely sized sands or ceramic particles, or in carbonate formations, permeability through fractures may be created by including acids in the fracturing which dissolve some minerals at the face of the fracture to create wormholes along the rock surfaces of the fractures. Proppants may be held in suspension within the fracturing fluids by including additives to increase the viscosity of the fracturing fluids, to decrease the settling rate of the proppants. Alternatively, or in addition, proppants may be utilized with lower densities to decrease the rate at which they settle in the fracture fluids,
Polymers used to increase the viscosity of fracturing fluids may be detrimental to formation permeability in the vicinity of the fractures, so techniques referred to as slick water fracturing have been developed. These techniques do not utilize thickening polymers, but instead rely on rapid injection of fracturing fluids.
Fracturing methods are disclosed in, for example, U.S. Pat. Nos. 8,183,179, and 7,451,820, the disclosures of which are incorporated herein by reference.
A method for providing permeability in fractures is described in U.S. Pat. No. 7,044,224. The method involves injecting a permeable cement composition, including a degradable material, into a subterranean formation. The degradation of the degradable material forms voids in a resulting proppant matrix. A problem of the method is that the degradation of the degradable material is difficult to manage. If the degradable material is not mixed uniformly into the cement composition, permeability may be limited. Furthermore, when degradation occurs too quickly, the cement composition fills the voids prior to forming a matrix resulting in decreased permeability. When degradation occurs too slowly, the voids lack connectivity to one another, also resulting in decreased permeability. In order for degradation to occur at the proper time, various conditions (such as pH, temperature, pressure, etc.) must be managed carefully, adding complexity and thus time and cost to the process. Another problem of the method is that the degradable material can be expensive and difficult to transport. Yet another problem of the method is that, even when large amounts of degradable material are used, permeability is only marginally enhanced. Furthermore, the addition of degradable material can have negative impact on flowability Fracturing formations with mortar compositions is known, for example, from US patent application publication US 2013/0341024.